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Ward CL, Cornejo MA, Peli Thanthri SH, Linz TH. A review of electrophoretic separations in temperature-responsive Pluronic thermal gels. Anal Chim Acta 2023; 1276:341613. [PMID: 37573098 DOI: 10.1016/j.aca.2023.341613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Revised: 07/10/2023] [Accepted: 07/11/2023] [Indexed: 08/14/2023]
Abstract
Gel electrophoresis is a ubiquitous bioanalytical technique used in research laboratories to validate protein and nucleic acid samples. Polyacrylamide and agarose have been the gold standard gel materials for decades, but an alternative class of polymer has emerged with potentially superior performance. Pluronic thermal gels are water-soluble polymers that possess the unique ability to undergo a change in viscosity in response to changing temperature. Thermal gels can reversibly convert between low-viscosity liquids and high-viscosity solid gels using temperature as an adjustable parameter. The properties of thermal gels provide unmatched flexibility as a dynamic separations matrix to measure analytes ranging from small molecules to cells. This review article describes the physical and chemical properties of Pluronic thermal gels to provide a fundamental overview of polymer behavior. The performance of thermal gels is then reviewed to highlight their applications as a gel matrix for electrokinetic separations in capillary, microfluidic, and slab gel formats. The use of dynamic temperature-responsive gels in bioanalytical separations is an underexplored area of research but one that holds exciting potential to achieve performance unattainable with conventional static polymers.
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Affiliation(s)
- Cassandra L Ward
- Department of Chemistry, Wayne State University, Detroit, MI, USA; Lumigen Instrument Center, Wayne State University, Detroit, MI, USA.
| | - Mario A Cornejo
- Department of Chemistry, Wayne State University, Detroit, MI, USA
| | | | - Thomas H Linz
- Department of Chemistry, Wayne State University, Detroit, MI, USA.
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Cornejo MA, Linz TH. Selective miRNA quantitation with high-temperature thermal gel electrophoresis. Anal Chim Acta 2023; 1275:341605. [PMID: 37524470 PMCID: PMC10390710 DOI: 10.1016/j.aca.2023.341605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2023] [Revised: 07/06/2023] [Accepted: 07/07/2023] [Indexed: 08/02/2023]
Abstract
MicroRNAs (miRNAs) are short non-coding RNAs that control gene expression and correlate to the prognosis of numerous diseases. To support research efforts elucidating the roles of miRNAs in pathogenesis, rapid and inexpensive analytical methods are required to quantify miRNAs from biological samples. The challenge of developing new analyses with these time and cost constraints is compounded by the short sequence lengths and high degrees of homology between miRNAs that hinder detection selectivity. This report describes the development of a high-temperature thermal gel electrophoresis (TGE) method to rapidly quantify miRNAs with single-nucleotide resolution using low-cost microfluidic devices. Fluorescent probes were designed for three miRNAs that differed in sequence by one or two nucleotides. A microfluidic analysis was optimized to enrich miRNA-probe hybrids into a high-concentration band and then automatically initiate a separation to resolve each species. Analyses conducted at 30 °C exhibited significant off-target hybridization, as the different-yet-structurally-similar miRNAs bound to each probe, which biased measurements. To overcome this problem, the stability of thermal gels at elevated temperatures was exploited to conduct analyses. At 50 °C, off-target hybrids melted to prevent their detection without impeding the enrichment or separation of on-target hybrids. Selectivity studies validated that high-temperature TGE prevented off-target hybrids from interfering with the quantitative responses of the target miRNAs. This work demonstrates that TGE affords rapid, highly selective analyses of structurally similar miRNAs in low-complexity microfluidic devices, which is expected to facilitate diverse biomedical research.
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Affiliation(s)
| | - Thomas H Linz
- Department of Chemistry, Wayne State University, USA.
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Peli Thanthri SH, Linz TH. Controlling the separation of native proteins with temperature in thermal gel transient isotachophoresis. Anal Bioanal Chem 2023; 415:4163-4172. [PMID: 36151350 PMCID: PMC10033466 DOI: 10.1007/s00216-022-04331-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 08/31/2022] [Accepted: 09/07/2022] [Indexed: 11/25/2022]
Abstract
Polyacrylamide gel electrophoresis (PAGE) is a ubiquitous technique used in biochemical research laboratories to characterize protein samples. Despite its popularity, PAGE is relatively slow and provides limited separation resolution, especially for native proteins. This report describes the development of a microfluidic thermal gel transient isotachophoresis (TG-tITP) method to rapidly separate native proteins with high resolution. Thermal gels were employed as a separations matrix because of their unique ability to change viscosity in response to temperature. Proteins were added into thermal gel and loaded into a microfluidic device. Electrolyte optimization was conducted to achieve robust tITP to isotachophoretically preconcentrate proteins and then electrophoretically separate them. Electropherograms were collected through both time and distance to enable both small and large proteins to be measured within a single analysis. The effects of temperature were evaluated and found to exhibit a pronounced effect on the separation. Temperature gradients were then employed to alter thermal gel viscosity over time to maximize separation resolution between proteins. The results herein demonstrate how gradient TG-tITP achieves rapid, high-performance separations of native proteins. This analysis provided a wide mass range (6-464 kDa) with two-fold higher resolution than native PAGE while requiring 15,000-fold less protein loading and providing five-fold faster analysis times.
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Affiliation(s)
| | - Thomas H Linz
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI, 48202, USA.
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Dos-Reis-Delgado AA, Carmona-Dominguez A, Sosa-Avalos G, Jimenez-Saaib IH, Villegas-Cantu KE, Gallo-Villanueva RC, Perez-Gonzalez VH. Recent advances and challenges in temperature monitoring and control in microfluidic devices. Electrophoresis 2023; 44:268-297. [PMID: 36205631 PMCID: PMC10092670 DOI: 10.1002/elps.202200162] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Revised: 09/22/2022] [Accepted: 10/03/2022] [Indexed: 11/07/2022]
Abstract
Temperature is a critical-yet sometimes overlooked-parameter in microfluidics. Microfluidic devices can experience heating inside their channels during operation due to underlying physicochemical phenomena occurring therein. Such heating, whether required or not, must be monitored to ensure adequate device operation. Therefore, different techniques have been developed to measure and control temperature in microfluidic devices. In this contribution, the operating principles and applications of these techniques are reviewed. Temperature-monitoring instruments revised herein include thermocouples, thermistors, and custom-built temperature sensors. Of these, thermocouples exhibit the widest operating range; thermistors feature the highest accuracy; and custom-built temperature sensors demonstrate the best transduction. On the other hand, temperature control methods can be classified as external- or integrated-methods. Within the external methods, microheaters are shown to be the most adequate when working with biological samples, whereas Peltier elements are most useful in applications that require the development of temperature gradients. In contrast, integrated methods are based on chemical and physical properties, structural arrangements, which are characterized by their low fabrication cost and a wide range of applications. The potential integration of these platforms with the Internet of Things technology is discussed as a potential new trend in the field.
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Affiliation(s)
| | | | - Gerardo Sosa-Avalos
- School of Engineering and Sciences, Tecnologico de Monterrey, Monterrey, Nuevo, León, Mexico
| | - Ivan H Jimenez-Saaib
- School of Engineering and Sciences, Tecnologico de Monterrey, Monterrey, Nuevo, León, Mexico
| | - Karen E Villegas-Cantu
- School of Engineering and Sciences, Tecnologico de Monterrey, Monterrey, Nuevo, León, Mexico
| | | | - Víctor H Perez-Gonzalez
- School of Engineering and Sciences, Tecnologico de Monterrey, Monterrey, Nuevo, León, Mexico
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Cornejo MA, Linz TH. Multiplexed miRNA Quantitation Using Injectionless Microfluidic Thermal Gel Electrophoresis. Anal Chem 2022; 94:5674-5681. [PMID: 35349277 DOI: 10.1021/acs.analchem.2c00356] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
MicroRNAs (miRNAs) are a class of biomolecules that have high clinical and pharmaceutical significance because of their ability to regulate protein expression. Better methods are needed to quantify target miRNAs, but their similar sequence lengths and low concentrations in biomedical samples impede analysis. This report aimed to develop a simple, rapid method to directly quantify multiple miRNAs using microfluidic thermal gel electrophoresis (TGE). Fluorescent probes were designed complementarily in sequence to four target miRNAs that also contained variable DNA overhangs to alter their electrophoretic mobilities. Samples and probes were directly added into thermal gel and loaded throughout a microchannel. Applying voltage resulted in an inline preconcentration and separation of the miRNAs that did not require a sample injection nor user intervention to switch between modes. Baseline resolution was achieved between four double-stranded miRNA-probe hybrids and four excess single-stranded probes. Analytical performance was then improved by designing an innovative microfluidic device with a tapered channel geometry. This device exhibited superior detection limits and separation resolution compared to standard channel devices without increasing the complexity of microfabrication or device operation. A proof-of-concept demonstration was then performed, showing that target miRNAs could be detected from cell extracts. These results demonstrate that TGE provides a simple, inexpensive means of conducting multiplexed miRNA measurements, with the potential for automation to facilitate future clinical and pharmaceutical analyses.
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Affiliation(s)
- Mario A Cornejo
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | - Thomas H Linz
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
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Butler D, Ebrahimi A. Rapid and sensitive detection of viral particles by coupling redox cycling and electrophoretic enrichment. Biosens Bioelectron 2022; 208:114198. [PMID: 35395617 PMCID: PMC8931995 DOI: 10.1016/j.bios.2022.114198] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 02/24/2022] [Accepted: 03/16/2022] [Indexed: 12/27/2022]
Abstract
The COVID-19 pandemic has highlighted the need for rapid, low-cost, and sensitive virus detection platforms to monitor and mitigate widespread outbreaks. Electrochemical sensors are a viable choice to fill this role but still require improvements to the signal magnitude, especially for early detection and low viral loads. Herein, finite element analysis of a novel biosensor concept for single virion counting using a generator-collector microelectrode design is presented. The proposed design combines a redox-cycling amplified electrochemical current with electrophoresis-driven electrode-particle collision for rapid virus detection. The effects of experimental (e.g. scan rate, collector bias) and geometric factors are studied to optimize the sensor design. Two generator-collector configurations are explored: a ring-disk configuration to analyze sessile droplets and an interdigitated electrode (IDE) design housed in a microchannel. For the ring-disk configuration, we calculate an amplification factor of ∼5 and collector efficiency of ∼0.8 for a generator-collector spacing of 600 nm. For the IDE, the collector efficiency is even larger, approaching unity. The dual-electrode mode is critical for increasing the current and electric field strength. As a result, the current steps upon virus capture are more than an order of magnitude larger compared to single-mode. Additionally, single virus capture times are reduced from over 700 s down to ∼20 s. Overall, the frequency of virus capture and magnitude of the electrochemical current steps depend on the virus properties and electrode configuration, with the IDE capable of single virus detection within seconds owing to better particle confinement in the microchannel.
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Affiliation(s)
- Derrick Butler
- Department of Electrical Engineering, The Pennsylvania State University, University Park, PA, 16802, USA; Materials Research Institute, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Aida Ebrahimi
- Department of Electrical Engineering, The Pennsylvania State University, University Park, PA, 16802, USA; Materials Research Institute, The Pennsylvania State University, University Park, PA, 16802, USA; Department of Biomedical Engineering, The Pennsylvania State University, University Park, PA, 16802, USA; Center for Biodevices, The Pennsylvania State University, University Park, PA, 16802, USA.
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